The invention relates generally to electrical machines and in particular, to a winding retention monitoring mechanism.
Armature windings, also known as stator bar windings, are routinely inspected in electrical power generators, to verify their operation. In some generators, a stator yoke in the generator surrounds an armature core and partially encloses the armature windings. The stator windings are formed from a plurality of copper conductors that are wound in the armature to form loops. The armature windings may be arranged within a stator slot in such a manner that the generator may maintain desired voltage and current characteristics during operation.
Typically, a generator includes a wedge system to induce a radial retaining force to the stator from wedges to facilitate reducing movement of the stator bar windings within the stator slot. However, if the wedge system itself becomes loose, the amount of retaining force is reduced such that the stator bar windings may move during operation. Over time, the relative motion of the stator bar windings cause damage to insulation surrounding the stator bar wedges and a potential stator bar winding failure through electrical shorts to ground. Accordingly, within generators, the wedge system is periodically inspected to determine if any stator bar winding movement within the stator slots exceeds predetermined tolerances.
Currently, several known methods of assessing the status of a wedge system are used. A first known method uses a hardness tester to assess the relative looseness of the stator wedges. A second known method requires tapping each individual wedge and listening to the response to determine whether the wedges are loose. A third known method includes exciting the vibrational modes of the stator wedges using multiple impacts, and receiving the energy transmitted from the multiple impacts using a band-pass filter to determine whether the wedges are loose. However, the aforementioned methods for determining the tightness of the wedge require offline measurements while the generator is not operational and do not predict the onset of loose wedges.
There is a need for an improved winding and wedge monitoring system to predict an onset of looseness. The monitoring system may further include features such as detecting temperature and partial discharge in the windings to help in preventive maintenance.